Brake systems for most modern vehicles consist of disc brakes, drum brakes or a combination of the two systems. An example of a disc brake system is a single-piston floating caliper (SPFC) system. The main brake corner components of a SPFC disc brake system are the brake pads, the caliper, the rotor, and the hydraulic brake circuit. The rotor is a plate-like disc that is configured to attach to, and rotates with, the hub of the vehicle wheel. The caliper is mounted adjacent the peripheral edge of the rotor and houses the brake pads and a single piston that is actuated by hydraulic pressure via the hydraulic brake circuit. When the brake pedal is pushed, hydraulic pressure increases and forces the piston of the caliper to extend outwardly. The extended piston causes the brake pads to be squeezed against both sides of the rotor whereby friction between the components bring the vehicle wheel to a stop.
Although similar in function to the disc brake system, a drum brake system utilizes different brake corner components which include, among other things, brake shoes instead of brake pads and a drum instead of a rotor. The drum is a bowl-like component that attaches to, and rotates with, the vehicle wheel. The brakes shoes are mounted inside of, and adjacent to, the walls that extend substantially perpendicular from the base of the drum. When the brake pedal of the vehicle is pushed, hydraulic pressure in the hydraulic brake circuit is increased. In response to the increased hydraulic pressure, a piston forces the brake shoes outward to engage the inside surface of the drum walls whereby friction between the components bring the vehicle wheel to a stop.
Brake pulsation feedback is an effect caused by a fluctuation in brake torque due to brake system corner component surface variations commonly referred to as Rotor Thickness Variation (RTV) and/or Drum Roundness Variation (DRV). Both RTV and DRV are frequently the result of variations in machining procedures but can also be caused by uneven wear of brake pads or shoes, corrosion, loose brake parts and/or uneven thermal expansion of brake corner components. The fluctuation in brake torque can also be a result of a non-uniform friction or frictional variations on the braking surface (non-uniform transfer film on the braking surface).
If the vehicle is equipped with an Anti-Lock Brake System (ABS), however, brake pulsation feedback and noise are normal during panic stops or when braking on wet or slick surfaces. But ABS brake pulsation feedback when braking normally on dry pavement does not occur. Accordingly, occurrence of such feedback during normal braking of an ABS-equipped vehicle could be indicative of a corner component having RTV or DRV.
If the vehicle has an Electro-Hydraulic Brake (EHB) system, it may utilize an Electro-Hydraulic Control (EHC) module rather than ABS module to control vehicle stopping. The EHB system eliminates the physical connection between the brake pedal and the hydraulic brake circuit. In such case, brake pulsation feedback due to RTV or DRV is noticeable through vehicle components other than the brake pedal such as the vehicle steering wheel, seats or other components.
In either case, brake pulsation feedback can be annoying to the driver of the vehicle, resulting in customer dissatisfaction and increased warranty claims. Additionally, efforts to eliminate brake pulsation feedback may be costly and time consuming, ranging from having to “turn” the rotors and/or drums to smooth the surfaces thereof, to having these components replaced altogether with the brake pads and shoes. Accordingly, it is desirable to have a brake system and method for minimizing brake pulsation feedback that occurs as a result of surface variations in brake system corner components.